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Retrieving the spectrum of physical radiation from experimental measurements typically involves using a mathematical algorithm to deconvolve the instrument response function from the measured signal. However, in the field of signal processing known as "Source Separation" (SS), which refers to the process of computationally retrieving the separate source components that generate an overlapping signal on the detector, the deconvolution process can become an ill-posed problem and crosstalk complicates the separation of the individual sources. To overcome this problem, we have designed a magnetic spectrometer for inline electron energy spectrum diagnosis and developed an analysis algorithm using techniques applicable to the problem of SS. An unknown polychromatic electron spectrum is calculated by sparse coding using a Gaussian basis function and an L1 regularization algorithm with a sparsity constraint. This technique is verified by using a specially designed magnetic field electron spectrometer. We use Monte Carlo simulations of the detector response to Maxwellian input energy distributions with electron temperatures of 5.0 MeV, 10.0 MeV, and 15.0 MeV to show that the calculated sparse spectrum can reproduce the input spectrum with an optimum energy bin width automatically selected by the L1 regularization. The spectra are reproduced with a high accuracy of less than 4.0% error, without an initial value. The technique is then applied to experimental measurements of intense laser accelerated electron beams from solid targets. Our analysis concept of spectral retrieval and automatic optimization of energy bin width by sparse coding could form the basis of a novel diagnostic method for spectroscopy.

We have developed an acceptance-cone-tunable (ACT) electron spectrometer for the highly efficient constant-energy photoelectron mapping of functional materials. The ACT spectrometer consists of the hemispherical deflection analyzer with the mesh-type electrostatic lens near the sample. The photoelectron trajectory can be converged by applying a negative bias to the sample and grounding the mesh lens and the analyzer entrance. The performance of the present ACT spectrometer with neither rotating nor tilting of the sample is demonstrated by the wide-angle observation of the well-known π-band dispersion of a single crystalline graphite over the Brillouin zone. The acceptance cone of the spectrometer is expanded by a factor of 3.30 when the negative bias voltage is 10 times as high as the kinetic energy of photoelectrons.

We present calculated and measured elastic and vibrational excitation cross sections in benzene with the objective to assess the reliability of the theoretical method and to shed more light on how the electronic motion of the incoming electron is coupled with the nuclear motion of the vibrations. The calculation employed the discrete momentum representation method which involves solving the two-channel Lippmann-Schwinger equation in the momentum space. The electron-molecule interaction was described by the exact static-exchange potential extended by a density-functional theory correlation-polarization interaction that models the molecular response in the field of the incoming electron. Cross sections were calculated for all 20 vibrational modes from near threshold until 20 eV. They were convoluted with a simulated instrumental profile for comparison with electron energy-loss spectra or appropriately summed for overlapping vibrations for comparison with measured cross sections plotted as a function of electron energy. An electron spectrometer with hemispherical analyzers was employed for the measurements. Good agreement of theory with experiment was obtained for the spectral profiles at 8 eV, and a nearly quantitative agreement was obtained at 3 and 4.8 eV. The theoretical results provided new insight into the excitation process, and it showed that more modes are excited than predicted by simple symmetry rules. Spectra showing the details of boomerang structure in the 1.15 eV π* resonance were recorded and are presented, although this aspect of experiment cannot be compared with the current theory.We present calculated and measured elastic and vibrational excitation cross sections in benzene with the objective to assess the reliability of the theoretical method and to shed more light on how the electronic motion of the incoming electron is coupled with the nuclear motion of the vibrations. The calculation employed the discrete momentum representation method which involves solving the two-channel Lippmann-Schwinger equation in the momentum space. The electron-molecule interaction was described by the exact static-exchange potential extended by a density-functional theory correlation-polarization interaction that models the molecular response in the field of the incoming electron. Cross sections were calculated for all 20 vibrational modes from near threshold until 20 eV. They were convoluted with a simulated instrumental profile for comparison with electron energy-loss spectra or appropriately summed for overlapping vibrations for comparison with measured cross sections plotted as a function of elec...

We present a newly developed magnetic-bottle time-of-flight electron spectrometer suitable for continuous or quasicontinuous photoionization sources such as synchrotrons. A strong magnetic field collects almost all photoelectrons from a well-defined ionization volume and quantitatively suppresses background electrons which originate outside of this interaction region. Although it is a pulsed instrument, a relatively high duty cycle is achieved by storing the photoelectrons generated between two cycles in an electromagnetic trap. This makes the new instrument suitable for experiments with very low sample densities. Another advantage is the high energy resolution, 50 meV in the first version of the spectrometer described here, which simply depends on the length of the time-of-flight instrument.

The measurement of angularly resolved energy distributions of mega-electron-volt electrons is important for gaining a better understanding of the interaction of ultra-intense laser pulses with plasma, especially for fast-ignition laser-fusion research. It is also crucial when evaluating the production of suprathermal (several 10-keV) electrons through laser-plasma instabilities in conventional hot-spot-ignition and shock-ignition research. For these purposes, we developed a 10-in. manipulator-based multichannel electron spectrometer-the Osaka University electron spectrometer (OU-ESM)-that combines angular resolution with high-energy resolution. The OU-ESM consists of five small electron spectrometers set at every 5°, with an energy range from ∼40 keV to ∼40 MeV. A low-magnetic-field option provides a higher spectral resolution for an energy range of up to ∼5 MeV. We successfully obtained angularly resolved electron spectra for various experiments on the OMEGA and OMEGA EP laser systems.

Variable-deceleration-ratio wide-acceptance-angle electrostatic lens (VD-WAAEL) is proposed as a potential technique for two-dimensional angular and energy analysis. The basic features of the lens are studied using the charge simulation method and ray tracing calculation. The lens uses an ellipsoidal mesh electrode and allows a wide acceptance angle of ±50°. Two possible applications of the VD-WAAEL are discussed. One is a simple combination of the VD-WAAEL-projection-lens, in which an aperture is used for energy analysis. The other is a combination of the VD-WAAEL with a conventional electron spectrometer, which is responsible for obtaining higher energy resolution. The former is discussed in detail and the latter is described briefly. While the ray tracing calculation is only for the case of an ideal mesh, a note on the disturbing effect of mesh holes is presented. The best possible energy resolution of the simple VD-WAAEL-projection-lens analyzer seems to be around 1/1000, given a fine mesh electrode to suppress the disturbing effect of mesh holes.

The energy distribution of electrons ejected from laser-induced plasma was measured using a magnetic spectrometer. The spectrometer was developed for quantitative analysis using an imaging plate. The efficiency of the imaging plate for detecting energetic electrons was calibrated using a transmission electron microscope, which accelerates electrons into energies between 80 and 200 keV. The kinetic energy distribution of electrons, which are ejected towards the backward direction, was measured on a copper bulk target irradiated with an infrared 60 fs laser. The obtained effective electron temperature in the energy range between 60 and 200 keV corresponded to approximately 130 keV at an intensity of 3.3×1017 W/cm2. This temperature was consistent with a scaling of 100[Iλ2/1017 (W μm2/cm2)]1/3 keV by Beg et al. [Phys. Plasma 4, 447 (1997)] derived from resonance absorption.

Neutrals desorbed from solid surfaces by electron beam impact can be ionized by the beam and trapped in the beam potential causing beam disruption. This can increase the beam diameter on radiographic bremsstrahlung targets degrading resolution. Measurements of the number and species of neutrals desorbed by impact of a 19.8 MeV, 1.7 kA, 60 ns electron beam on thin-foil targets are made in open and closed geometries. The study focuses on aluminum and graphite foil surfaces. A fast Bayard–Alpert ionization gauge measures the number of neutral molecules released, and a quadrupole mass spectrometer measures the species mix. At high beam current density, where thermal desorption due to target heating is expected, the dominant neutral species is H2O, and approximately one monolayer of desorbed gas is released. Other prominent species such as H2, CO, and CO2 are not thermally desorbed until current densities near foil destruction are approached. The observations are in agreement with a previous hypothesis based o...

A highly efficient time-of-flight electron spectrometer is described. An incident electron current of the order of 10−14 A makes it suitable for studying secondary emission from dielectric surfaces. A microchannel plate position-sensitive detector allows flight distance correction while keeping a large acceptance angle. Measured energy distribution curves of secondary electrons generated from a LiF film by 19–31 eV incident electrons demonstrate good energy resolution and reveal reproducible and stable emission features at 2.6±0.3 eV, 7.2±0.3 eV, and 10.3±0.3 eV.

The energy distribution of electrons transported through intrinsic AlN heteroepitaxial films grown on SiC was directly measured as a function of applied field and AlN film thickness. Following the transport, electrons were extracted into vacuum through a semitransparent Au electrode and their energy distribution was measured using an electron spectrometer. Transport through films thicker than 95 nm at an applied field between 200 and 350 kV/cm occurred as steady-state hot electron transport following a Maxwellian energy distribution with a characteristic carrier temperature. At higher fields (470 kV/cm), intervalley scattering was evidenced by a multicomponent energy distribution featuring a second peak at the energy position of the first satellite valley. Velocity overshoot was observed in films thinner than 95 nm and at fields greater than 550 kV/cm. In this case, a symmetric energy distribution centered at an energy above the conduction band minimum was measured, indicating that the drift component of ...

For the purpose of end-loss-ion energy analyses in open-field plasmas, a newly developed electrostatic ion-energy spectrometer is proposed on the basis of a “self-collection” principle for secondary-electron emission from a metal collector. The ion-energy spectrometer is designed with multiple grids for analyzing incident ion energies, and a set of parallelly placed metal plates with respect to lines of ambient magnetic forces in an open-ended device. One of the most important characteristic properties of this spectrometer is the use of our proposed principle of a “self-collection” mechanism due to E×B drifts for secondary electrons emitted from the grounded metal-plate collector by the use of no further additional magnetic systems except the ambient open-ended fields B. The proof-of-principle and characterization experiments are carried out by the use of a test-ion-beam line along with an additional use of a Helmholtz coil system for the formation of open magnetic fields similar to those in the GAMMA 10 end region. The applications of the developed ion-energy spectrometer for end-loss-ion diagnostics in the GAMMA 10 plasma experiments are demonstrated under the conditions with simultaneous incidence of energetic electrons produced by electron-cyclotron heatings for end-loss-plugging potential formation, since these electrons have contributed to disturb these ion signals from conventional end-loss-ion detectors.For the purpose of end-loss-ion energy analyses in open-field plasmas, a newly developed electrostatic ion-energy spectrometer is proposed on the basis of a “self-collection” principle for secondary-electron emission from a metal collector. The ion-energy spectrometer is designed with multiple grids for analyzing incident ion energies, and a set of parallelly placed metal plates with respect to lines of ambient magnetic forces in an open-ended device. One of the most important characteristic properties of this spectrometer is the use of our proposed principle of a “self-collection” mechanism due to E×B drifts for secondary electrons emitted from the grounded metal-plate collector by the use of no further additional magnetic systems except the ambient open-ended fields B. The proof-of-principle and characterization experiments are carried out by the use of a test-ion-beam line along with an additional use of a Helmholtz coil system for the formation of open magnetic fields similar to those in the GAMMA 10 ...

We describe a prototype of a novel electron spectrometer that employs a two-dimensional tomographic method to obtain the electron velocity distribution in a space plasma. The spectrometer consists of a magnetic field cavity with a single entrance aperture and a one-dimensional position sensitive microchannel plate/anode assembly electron detector. Electrons entering the instrument through the aperture which have the same component of velocity normal to the aperture plane will all strike the electron detector at the same location regardless of the magnitude of the other velocity component. Thus, the instrument performs line integrals in velocity space. By placing the instrument on a spinning spacecraft, it will provide a complete set of these integrals that may be deconvoluted using standard tomographic techniques. In many cases, basic plasma parameters can be inferred directly from the raw data without deconvolution. This instrument has advantages over conventional electrostatic analyzers: it does not require power consuming voltage stepping, makes efficient use of volume, and operates with a high duty cycle. A modified version of the instrument that is insensitive to photons and can determine three-dimensional distribution functions is also described.

We report on experimental advances in scanning electron microscopy with polarization analysis that allow the observation of ferromagnetic domains in external magnetic fields of about 0.1 T. This is achieved by using a modified electron optics that produces a magnetic field at the sample surface that is spatially confined on the length scale of 0.1 mm. During imaging, primary and secondary electrons pass through the magnetic field without significant disturbance. We demonstrate that the primary electron beam may be used to keep track of the generated magnetic field. As an exemplary application, the switching processes of rectangular Permalloy elements are analyzed.

The interaction of a high current relativistic electron beam with solid targets is analyzed. The conditions of the beam separation from the target are presented and the energy losses due to collective effects are evaluated for the cases of metals and dielectrics. The energy losses in dielectrics are higher because of the ionization of atoms in the beam self-consistent electric field. The problem of ion acceleration at the solid-vacuum interface is also considered.

We present experimental results of the generation of a high-frequency modulated electron beam in a diode with a ferroelectric plasma cathode. The energy of electrons in the modulated beam is significantly higher than that obtained in previous experiments, reaching 150 keV. The maximum amplitude of the modulated beam current reaches 65 A, which corresponds to a beam power of 4.5 MW. Data concerning the influence of the diode geometry and the accelerating voltage on the electron energy and the amplitude of the modulated beam current are presented. It was found that the beam modulation is caused by the variation of the beam electron density, and that it has uniform cross-sectional electron beam current density distribution. Efficient transport of the modulated electron beam in a guiding external magnetic field without distortion of its waveform is demonstrated. The electron beam modulated at 190 MHz with an amplitude of 25 A was transported in the magnetic field (0.3–3 kG) along a distance of 50 cm. In addit...

Radial-radiated electron beam is widely employed in radial-line structure microwave devices. The quality of the electron beam has a crucial effect on the operating performance of these devices. This paper analyzes theoretically this electron motion in a radial-line drift tube with finite magnetic field conducted. The beam width, spatial period, and fluctuation amplitude are quantitatively analyzed with different beam current parameters. By the particle-in-cell simulation, we examine the theoretical analysis under the condition of a designed realistic coil configuration. It indicates that the derived beam envelope function is capable of predicting the radial-radiated beam trajectory approximately. Meanwhile, it is found that the off-axial z-direction magnetic field, in spite of its greatly slight amplitude, is also one necessary consideration for the propagation characteristic of the radial-radiated electron beam. Furthermore, the presented electron motion analysis may be instructive for the design of the ...

In an energy-dispersive electron spectrometer, the electrons with the same kinetic energy but different polar angles fly along different paths and impinge upon the detector at different locations. This behavior materializes the spherical aberration of the electron optics, which deteriorates the focussing quality on the detector, and thus the energy resolution of the instrument. Here, we demonstrate that, in general, the electron time of flight changes monotonically as a function of the polar angle. Combining the impact position on the detector and the time of flight of electrons, the spherical aberration can be corrected and the energy resolution can be significantly improved, 1.5× in the case of our double toroidal analyser. This correction method has a general applicability and can be of interest to experimentalists willing to push further the performances of their electron spectrometers when the time of flight is available.

The electronic properties of gold–silver binary cluster anions (AunAgm−; 2⩽n+m⩽4) were studied by using photoelectron spectroscopy (PES) with a magnetic-bottle-type electron spectrometer. The AunAgm− cluster anions were generated by a laser vaporization of a gold–silver alloy rod. For triatomic AunAg3−n clusters, monotonous increases of electron affinity (EA) were observed by the replacement of Ag atom by Au atom. In contrast, the change in EA of tetratomic AunAg4−n clusters was irregular; for n=0–2 their EAs are almost the same around 1.5 eV, whereas for n=3,4 they increase to around 2.7 eV. This irregularity in EA of AunAg4−n can be attributed to the contribution of an ionic bonding. For Au1Ag3− and Au2Ag2−, moreover, the PES spectra show two components whose intensity ratio depends on cluster source conditions, showing that two isomers should coexist at these two compositions.

Electrons ionized from tightly bound atomic states by a high-intensity laser pulse can gain energies from one to millions of electron volts dependent on the intensity of the pulse. We have currently been investigating hundreds of kilovolt to megavolt electrons produced by ionization of krypton and argon with terawatt laser pulses. Angular and energy distributions have been measured to determine the usability of this electron source as an injector for higher energy accelerators. Studies have included pressure dependence, angular ejection angle energy dependence, and polarization dependence. In particular, the energy-dependent ejection angle of electrons has been used to produce electron beams with energies peaked at 600 keV. Numerical simulations of these electrons show that 4 MV electron beams with excellent beam quality and femtosecond pulse widths can be produced from this electron source using higher power laser pulses.

The generation of fast electron beam pulses by voltages in the range of 1 V is presented. Two emission mechanisms are described, where the one which utilizes thermal electron confinement in the proximity of a sharp filament proves to be more advantageous. We have observed pulsewidth of 5 ns, limited only by our recording instruments. Due to the superb optical quality and tunability, this electron beam modulation mechanism can find applications in time-resolved diffraction/imaging, microwave system, time-of-flight spectrometer, and electron beam lithography.

We present a very efficient 90° sector magnet mass spectrometer detector, based on electron impact ionization, especially adapted for the use with atomic and molecular beams. In this setup, a cylindrically symmetric magnetic field compresses electrons emitted from a large filament into a long, narrow volume containing primarily the molecular beam. This has the advantage of both producing as little as possible background from residual gases and increasing the interaction region between beam and ionizer. Experimental tests using thermal He atoms show that the detector’s efficiency and sensitivity are very high, amounting to η⩾0.70±0.04% and S=0.22±0.03 A mbar−1, respectively. The unconventionally long ionization volume, however, may restrict the use of this mass spectrometer to experiments with no, or only moderate timing requirements.

Penning ionization electron spectra (PIES) of van der Waals clusters have been observed for the first time by means of a newly developed magnetic bottle electron spectrometer, which is 1000 times more efficient than a conventional PIES apparatus. In the PIES of Ar clusters with He*(2 3S), two bands of Ar 3p hole characters with different ionization energies (IE), band A (IE=ca.15 eV) and band B (IE=ca.13.5 eV), were observed. Band A was assigned to vertical transitions in Franck–Condon regions corresponding to the band in the ultraviolet photoelectron spectra (UPS) of clusters reported by Carnovale et al. [J. Chem. Phys. 90, 1452 (1989)]. Band B, which is an extra band missing in the UPS of clusters, can be ascribed to the autoionization into a stable structure of Arn+ via superexcited states of Arn. Band B can be considered as an adiabatic ionization which is forbidden as a direct ionization. The energy difference of ca. 1.5 eV between the vertical IE for band A and the adiabatic IE for band B was found ...

We have developed a magnetic spectrometer to characterize the hot electrons generated in high-intensity (>1018 W/cm2) laser-plasma interaction experiments. It comprises a dispersive element consisting of a permanent dipole magnet and an electron detector incorporating 45 scintillating/light-guiding plastic fibers connected to a cooled charged-coupled device camera. The main features of this instrument are high spectral resolution, low sensitivity to x and γ rays, and versatility due to its compact design. Performance and operational capabilities are illustrated based on experimental results in which electron energy–spectra in the range of 520 keV to 12.6 MeV were obtained with an energy resolution of 10% and a detection threshold of 106 electrons per MeV.

New double-resonance ionization data are presented on the autoionizing Rydberg states of NH3 excited via selected rotational levels of the C′ 1A1(0100) and (0200) states. Extrapolation of the Rydberg series provides a determination of the adiabatic ionization energy of NH3 that is in excellent agreement with that obtained by using zero kinetic energy photoelectron spectroscopy (ZEKE-PES). A comparison is presented between the field-free spectrum obtained by using a time-of-flight mass spectrometer and the 1-Tesla-spectrum obtained by using a magnetic-bottle electron spectrometer. Finally, the rotational and vibrational autoionization mechanisms are discussed.

We have developed an efficient electron time-of-flight (TOF) selection scheme for high resolution pulsed field ionization (PFI) photoelectron (PFI-PE) measurements using monochromatized multibunch undulator synchrotron radiation at the Advanced Light Source. By employing a simple electron TOF spectrometer, we show that PFI-PEs produced by the PFI in the dark gap of a synchrotron ring period can be cleanly separated from prompt background photoelectrons. A near complete suppression of prompt electrons was achieved in PFI-PE measurements by gating the PFI-PE TOF peak, as indicated by monitoring background electron counts at the Ar(11s′) autoionizing Rydberg peak, which is adjacent to the Ar+(2P3/2) PFI-PE band. The rotational-resolved PFI-PE band for H2+ (X 2Σg+,v+=0) measured using this electron TOF selection scheme is nearly free from residues of nearby autoionizing features, which were observed in the previous measurement by employing an electron spectrometer equipped with a hemispherical energy analyzer...

A crossed-beam collision geometry has been successfully applied to a double trochoidal electron spectrometer. In order to improve the efficiency of the instrument, an original design of the sample gas inlet system has been developed. The instrument has been tested by measuring low energy vibrational excitation of the nitrogen molecule. A high energy resolution and a high sensitivity have been achieved. Obtained spectra exhibit some new structure, not previously recorded in a similar measurements.

New results on the competition between autoionization and predissociation in the high Rydberg states of nitric oxide are presented. These results provide insight into the earlier work of Park et al. [Phys. Rev. Lett. 76, 1591 (1996)] that shows evidence for substantial mixing between Rydberg series and ionization continua with even and odd orbital angular momenta (l). New data based on fluorescence-dip spectroscopy, detection of neutral predissociation products, and photoelectron spectroscopy suggest that the A′ 2Σ+ and I 2Σ+ dissociative valence states play an important role in this l mixing. Zeeman splittings observed in a magnetic bottle electron spectrometer also result in an improvement in the assignment of these high Rydberg states.

The setup of an electron spectrometer for angle-resolved photoemission is described. A sample goniometer offers the opportunity for angle scanned photoemission over 2π solid angle above the surface. A monochromatized high flux He discharge photon source is exploited to measure thermally populated electronic states above the Fermi level EF. At energies greater than EF+5kBT the signal from a constant density of states declines below the photoelectron background caused by photons with higher energies than He Iα (21.2 eV). For He IIα (40.8 eV) the residual photoelectron background is lower and photoemission up to 6kBT above EF can be performed. Data showing two cuts through the Fermi surface of silver are presented. Furthermore the dispersion of the Shockley surface state on Ag (111) above the Fermi energy is quantified.

We have developed a new compact retarding-potential Mott spin polarimeter and achieved an efficiency of 1.9×10−4 for gold target operating in 25 keV. A novel design of the retarding field electron optics with 0.59 sr collection solid angle for scattered electrons was adopted based on Monte Carlo calculations for the spin-dependent electron scattering process and electron beam ray-tracing calculations. We have combined the new spin polarimeter with an angle-resolved photoelectron spectrometer and measured the spin- and angle-resolved photoelectron spectra and studied the spin-dependent electronic structure of Ni(110) along the ΓS line of its surface Brilluoin zone.

In this article we describe the design and the operation of an original, high transmission, electrostatic “double toroidal” electron energy analyzer. The double toroidal analyzer allows the high resolution and high luminosity simultaneous measurement of the kinetic energy, and angular distribution of electrons, using a two-dimensional position sensitive detector. The exact shape of the electrodes is deduced from both analytical and numerical electron trajectory calculations. The electron detector is based on a charge analysis and optimized to attain a 100 kHz counting rate. The actual performances of the analyzer are illustrated with spectra obtained after resonant Auger decay of N2O excited around the nitrogen K shell (hν=401 eV), and of Kr after 3d5/2→5p excitation at hν=91.2 eV. A “etendue” of 15% of the pass energy, as well as a resolving power (Ep/δE) of 100 were measured.

The propagation of an annular intense relativistic electron beam inside a cylindrical drift tube is affected by many factors such as external magnetic field, drift tube geometry, the beam self electric and magnetic fields, etc. It is shown, experimentally and theoretically, that the deleterious influence of the self‐fields on the electron flow can be reduced when part of the beam return current is allowed to flow on a grounded conductor that is inserted coaxially within the beam. The improvement manifested itself by reducing the axial magnetic field needed to confine the electron beam or alternately by lowering the electron transverse velocities.

A warm beam is produced by passing a cold electron beam through a system of three closely spaced parallel grids. The beam and the grid structure are immersed in a magnetic field. The middle grid is biased at a large positive potential, and the resulting electric field near the grid wires scatters part of the electrons axial energy into transverse energy. Thus, although the beam remains monoenergetic, a controllable spread in both the transverse and axial energy distribution is obtained.

Iron–sulfur cluster anions (FenS−m, n=1–6, m=1–6) have been studied using photoelectron spectroscopy (PES) with a magnetic‐bottle‐type time‐of‐flight electron spectrometer. The FenS−m cluster anions were formed in a laser vaporization cluster source. It was found that the stable cluster ions are the ones with compositions of n=m and n=m±1. The electron affinities were measured from the onsets of the PES spectra. Three low‐lying electronic states were observed for FeS. The PES spectra of FenS− (n=1–4) series show a unique similarity, indicating that the Fe atom addition to FeS− has little effect on the electronic property of FeS. The PES spectra of FenS−2 series show a similarity among the cluster anions with n=2–4, showing that Fe2S−2 is the structural framework of these clusters. For FenS−3 series, Fe3S−3 is proposed to be the structural framework. The electronic properties and geometrical structures of the clusters are discussed.

Time-resolved electron-beam diagnostics have been developed for use with free-electron lasers (FELs) and associated electron sources, based on the techniques of secondary electron emission and optical transition radiation (OTR). The 32-channel OTR detector forms part of a high-resolution (0.18%) electron spectrometer with a time resolution of 50 ns. Variable-magnification optics allow the spectrometer to view single-macropulse spectra with widths in the range of 0.2%-7%; wider spectra are taken with several momentum settings. Design criteria for the spectrometer are presented, and experience of operating with the diagnostics over a range of FEL physics experiments is summarized. The spectrometer is used, in conjunction with optical diagnostics, in studies at FELIX of efficiency enhancement, pulse chirping, and stepped-undulator operation. (C) 1996 American Institute of Physics.

A compact high-resolution ({lambda}/{Delta}{lambda} {approx} 10000) spherically bent crystal spectrometer in the Johann geometry was recently installed and tested on the Lawrence Livermore National Laboratory SuperEBIT electron beam ion trap. The curvature of the mica (002) crystal grating allows for higher collection efficiency compared to the flat and cylindrically bent crystal spectrometers commonly used on the Livermore electron beam ion traps. The spectrometer's Johann configuration enables orientation of its dispersion plane to be parallel to the electron beam propagation. Used in concert with a crystal spectrometer, whose dispersion plane is perpendicular to the electron beam propagation, the polarization of x-ray emission lines can be measured.

Photoelectron spectra of SinC−m cluster anions (1≤n≤7 and 1≤m≤5) were measured at the photon energies of 3.49 eV, by using a magnetic bottle electron spectrometer. The SinC−m clusters were produced either by a laser vaporization of a silicon–carbon mixed rod or by two laser vaporizations of carbon and silicon rods in a He carrier gas. The spectra of the SinC−1 (3≤n≤7) clusters are similar to those of pure Si−n+1 clusters in the peak positions and their envelopes, which is attributed to the isovalent electronic structure of Si and C atoms as well as to the similar geometrical structure. In contrast, the similarity in the photoelectron spectra is not observed between C−m+1 and Si1C−m (2≤m≤5) clusters, which is attributed to a change in their geometry; from chain to ring. These experimental conclusions are discussed with the results of our theoretical calculations.

An (e,3e) spectrometer for the study of double ionization of magnesium by electron impact is described. With the spectrometer the angular and energy distributions of the ejected electrons can be measured over a range of incident‐electron energies. The spectrometer incorporates two ejected‐electron electrostatic energy analyzers and a tandem electrostatic analyzer for the scattered electrons. Up to eight detectors can be placed at the focal planes of each of the ejected analyzers. This increases the data rate by a factor of 64 over arrangements with two ejected‐electron detectors. In order to reduce noise and establish the energy of the final state of the doubly charged residual magnesium ion, triple‐coincidence electronics are used with a preprocessing circuit to reduce dead time. The first double‐ionization study with the instrument was the ejection of a 2p inner valence electron by a 3.5 keV incident electron accompanied by the subsequent filling of the 2p hole and the emission of a 35 eV Auger electron.

Photoelectron spectra of AlnS−1 (1≤n≤9) cluster anions were measured at the photon energies of 3.49 and 4.66 eV, using a magnetic bottle electron spectrometer having ∼60 meV resolution. AlS− has an electron affinity of as large as 2.6 eV, attributed to large stability by six bonding electrons. A new electronic state, A’ 2Π, was found 0.4 eV above the AlS ground state, which is in agreement with theoretical calculations. AlnS−1 cluster anions are produced efficiently up to n=5, but the production of larger cluster sizes is found difficult. The mass distribution of AlnS−1 cluster anions and electron binding energy can be explained by a geometric structure obtained by theoretical calculation.

Ultraintense laser-matter interactions provide a unique source of temporally short, broad spectrum electrons, which may be utilized in many varied applications. One such, which we are pursuing, is as part of a diagnostic to trace magnetic field lines in a magnetically confined fusion device. An essential aspect of this scheme is to have a detailed characterization of the electron angular and energy distribution. To this effect we designed and constructed a compact electron spectrometer that uses permanent magnets for electron energy dispersion and over 100 scintillating fibers coupled to a 1024×1024 pixel charge coupled device as the detection system. This spectrometer has electron energy coverage from 10 keV to 60 MeV. We tested the spectrometer on a high intensity (1017–1021 W/cm2) short pulse (

An electron momentum spectrometer has been constructed which measures electron binding energies and momenta by fully determining the kinematics of the incident, scattered, and ejected electrons resulting from (e,2e) ionizing collisions in a thin solid foil. The spectrometer operates with incident beam energies of 20–30 keV in an asymmetric, non‐coplanar scattering geometry. Bethe ridge kinematics are used which for 20 keV incident energy has scattered electron energies of 18.8 keV at a polar angle of θs=14°and azimuthal angles φs in the range from −18° to +18° and ejected electrons of 1.2 keV and θe=76°with φe=π±6°. The technique uses transmission through the target foil, but it is most sensitive to the surface from which the 1.2 keV electrons emerge, to a depth of about 2 nm. Scattered and ejected electron energies and azimuthal angles are detected in parallel using position sensitive detection, yielding true coincidence count rates of 6 Hz from a 5.5 nm thick evaporated carbon target and an incident bea...

Design improvements of a toroidal sectoral backscattered electron energy spectrometer adapted for application in the scanning electron microscope were made. Various geometrical parameters in the design of the spectrometer were optimized on the basis of simulation and improvement in the energy resolution of the spectrometer by more than a factor of 2 was confirmed by experiment.

A coplanar electron spectrometer has been constructed for angle‐resolved electron energy loss measurements. The experimental arrangement and performance of the spectrometer are described. Absolute absorption transition probabilities (or generalized oscillator strengths) of valence‐shell (7–70 eV) electronic transitions of SF6 have been determined as a function of energy loss and momentum transfer at an impact energy of 2.5 keV. New nondipole transitions have been observed at nonzero momentum transfer. Together with the term values obtained from previous dipole electron energy loss and photoabsorption measurements, the momentum transfer dependence of the transition probabilities can be used to provide tentative assignments of the observed nondipole valence‐shell transitions of SF6. Despite the complexity of the electronic structure of SF6, the present work demonstrates the feasibility of angle‐resolved electron energy loss spectroscopy for investigating nondipole phenomena and related electron‐induced exci...

This paper develops theoretical expressions to study angular distribution and spin polarization of those Auger electrons which are emitted in the decay of a vacancy created by the absorption of a photon in a rotating linear molecule. Identical expressions except, of course, for different decay amplitudes, in both the Hund’s coupling schemes (a) and (b), are obtained for the differential Auger current emitted in the transition J→Jf measured by an electron spectrometer sensitive to spin detection. The structure of these angular distributions is exactly the same as that of the spin‐resolved photoelectrons from unoriented atoms and molecules. The present paper thus puts the angle‐ and spin‐resolved Auger and photoelectron spectroscopies on the same footing wherein identical geometrical and kinematical analysis is applicable. The four parameters needed to completely characterize such distributions depend, in the present case, on rotational orientation and/or alignment of the photoexcited molecule, in addition ...

An improved spectrometer design for photoelectron yield spectroscopy is described. Basis of the new spectrometer is a computer‐designed electron optics that images the emission spot into the electron multiplier and thereby improves the sensitivity for electrons emitted from the sample. The collection efficiency was experimentally determined to 98.3%. A background of stray electrons which limits the ultimate sensitivity of the method could be substantially reduced by minimizing multiple beam reflections and by coating critical surfaces with a high work function material such as platinum. As a result, photoyield spectra of Au with a dynamical range of ten orders of magnitude are routinely obtained.

The performance of a spherical field-free and a conical retarding-potential Mott polarimeter is compared. The stability of the detector signal with respect to a change in the position of the incoming electron beam is studied for two different primary electron beam energies. Shifting the incoming electron beam by 0.6 mm does not change the counting rate in the spherical field-free detector but induces a 7% or 18% change in the conical retarding-potential detector when using 1600 and 500 eV electrons, respectively. This may result in an error of the measured electron spin polarization.

We describe an angle‐resolving photoelectron spectrometer for atoms and molecules which uses the magic angle geometry in combination with multidetection such that cross sections and asymmetry parameters can be determined simultaneously. The instrument is based on the cylindrical mirror analyzer (CMA) design with the cylinder axis and the light beam collinear. Only the photoelectrons which are emitted in the ‘‘reverse’’ direction at the magic angle reach the ring‐shaped position‐sensitive detector. The complete system also incorporates a conical effusive gas source, in order to maintain cylindrical symmetry, and very efficient differential pumping between target and electron spectrometer. Results from the C 1s photoionization of CO2 demonstrate the kind of precision attainable.

An electron string is a state of a one component electron plasma, which can arise when multiply reflected electrons are accumulated in a strong solenoidal magnetic field. Based on the electron beam ion source (EBIS) in the reflex mode of operation the processes of the string formation and its decay were observed and the characteristic times of the processes have been measured. Information about the electron energy distribution in electron strings has been obtained using four independent methods. It was shown, the distribution is broad and, moreover, there is some amount of electrons, having energies higher than the energy of the electrons used for feeding the string. An instability was observed as a starting point of electron string formation. The instability is strongly suppressed and the string is formed when the injecting electron current reaches a threshold value, which depends on a quality of electron focusing. Most likely the instability observed is responsible for the string electron energy spread....

Extensive modifications of an electrostatic electron spectrometer of the hemispherical type are described. The purpose of the modifications is to make the instrument more suitable for high‐resolution gas phase spectroscopy. The changes concern substitution of electrical adjustments for mechanical precision, improved flexibility in focusing, and a new system of computer‐controlled power supplies and detector interface. The instrument is also used for energy analysis of positive ions. Conversion between positive and negative particle analysis is achieved simply by reversing the polarities of all relevant voltages by a number of switches. A gas cell with internal heating is described. The influence of gas cell conditions on resolution is briefly discussed. The computer programs used for spectrometer control, data acquisition, spectrometer optimization, and calibration are described.

Measurements for axially incident electrons are reported for the energy and spatial dependencies of the detection efficiency of a Philips X919BL single channel electron multiplier (CEM) in both the pulse counting and analog amplification modes. The behavior may be understood in terms of the general theory reported earlier.1 Essentially there are three regions to consider: the horn, the channel and the edge of the channel. In the pulse counting mode the difference in efficiencies between the channel and horn may reach a factor of two whereas in the analog mode the difference between the channel edge and the horn may reach a factor of five. The same behavior occurs when the CEM is used as the output stage of an electron spectrometer. The above variations may lead to (i) loss of efficiency in spectrometers, (ii) spectral distortion arising from the associated presence of stray magnetic fields, and (iii) irreproducibility of spectra from different regions of the sample surface, unless specific measures, such as larger horns, off‐axis channels or lens defocusing, are used to eliminate them.

Investigated are the effects of longitudinal electron temperature on the eigenmodes of a high gain Compton free-electron laser. It is noted that the electron beam temperature reduces the growth rate by destroying the refractive guiding property of the electron beam.